The invention relates to machining gears and in particular to a process for machining the flanks of gearing which is more or less cylindrical but is modified to widen the crown, in a continuous diagonal hobbing process.
Warped flanks occur during generation of helical wide-crowned cylindrical gears in the continuous hobbing process. The offset is a gauge of the warping.
To solve this problem, DE 37 04 607 (corresponding to U.S. Pat. No. 4,850,155 to Sulzer) discloses machining of the gearing in the continuous diagonal hobbing process and in the process using a helical tool whose pressure angle decreases continuously from a maximum value at one end of the worm toward the other end, the maximum pressure angle of the right flank at one end of the worm coinciding with the minimum pressure angle of the left flank and vice versa. Manufacture of this tool is extraordinarily costly.
The Gear Production Practice seminar held at the Technische Akademie Esslinger, Mar. 25 to 27, 1996, also discloses design of the grinding worm so as to be laterally concave, use of this worm in the diagonal process, and derivation of the information necessary for analysis from a special xe2x80x9ccrowning envelope.xe2x80x9d This crowning curve is represented over a reference plane which is positioned tangentially to a cylinder concentric with the gear axis; this is presumably a partial cylinder. A crowning envelope such as this is unknown. In other respects as well it appears not to be possible to merge the differently warped crowning envelopes of the two flanks in a common envelope.
The following discussion will also show that use of a concave-crown worm in the diagonal process itself again results in crown concavity. Consequently, proper equalization of the surface or selective production of a desired offset cannot be accomplished exclusively through design of the tool.
It is an object of the present invention to prevent the warping offset or to produce an offset of the flanks which differs from the xe2x80x9cnatural offset.xe2x80x9d
The present invention is based on the technical problem of developing the generic process so that flanks modified to be broad-crowned can be produced with virtually any offsets in the one-flank or two-flank process, so that geometrically simple tools may be used, so that theoretically exact results are obtained even after shifting of the tool, and so that the active tool length required for machining a workpiece may be freely selected over a wide range.
The crown width desired and the offset desired can be obtained at the workpiece in a simple manner and with geometrically simple tools, by adjustment of tool lead modification, the axial spacing between tool and workpiece, or the angle of rotation.
The invention is explained in detail on the basis of embodiments illustrated in the accompanying drawings.